NMT 900 (Nordic Mobile Telephone 900 MHz) A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries. NMT 900 operates in the 900 MHz band, employing frequency division multiple access (FDMA) to derive 1999 channels with a width of 12.5 kHz. NMT 900 employs frequency division duplex (FDD) to achieve bidirectional communications, with the downlink in the 935-960 MHz band and the uplink in the 890-915 MHz band.Within each channel, frequency modulation (FM) is employed. See also 1G, analog,cellular radio, channel, downlink, FDD, FDMA, FM, and uplink. NN (Network Neutrality) Referring to Internet neutrality. See Net neutrality. NNI (Network-to-Network Interface) The boundary or point of interaction between network serv- ice providers.The NNI is both a physical and logical point of demarcation.The NNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the individual service providers. NNIs are defined for asynchronous transfer mode (ATM) and frame relay, as examples. See also ATM, logical, frame relay, physical, and protocol. NOC (Network Operations Center) (pronounced knock) Also known as network control center (NCC). A centralized location from which a large, complex network and its component subnetworks and network elements can be monitored, and faults or performance failures can be identified, diagnosed, isolated, and often corrected. See also network, network element, and subnet. node 1. A junction point at which two or more circuits interconnect in a data network. A bridge, for example, interconnects two or more segments of a local area network (LAN). See also bridge, circuit, LAN, and network. 2. In a switched network, a switching point that comprises a point of interconnection for cir- cuits, a data switch, and control facilities. In the public switched telephone network (PSTN), for example, a great many circuits terminate in a central office (CO) and a tandem office, each of which comprises one or more switches and Signaling System 7 (SS7) network control logic, multiplexers, a wide variety of other devices. See also access node, CO, PSTN, service node, SS7, switch, and tandem switch. 3. A device such as a sta- tion, bridge, computer, repeater, server, switch, or other device that connects to a network. 4. In the IBM Systems Network Architecture (SNA), a physical device such as a computer, communications processor (e.g., FEP), terminal controllers, or terminal. See also SNA. noise Unwanted disturbances superimposed on a signal and interfering with its integrity. Noise can be introduced by equipment or can be the result of natural phenomena. Noise can take a number of forms, including amplitude noise, cross-talk,echo,intermodulation noise,harmonic distortion, impulse noise,ran- dom noise, and white noise. nominal In name only, but not in reality.A T1 circuit sometimes is described as having a nominal trans- mission rate of 1.5 Mbps,although in reality the signaling rate is 1.544 Mbps and its payload is 1.536 Mbps. It is easier to say one point five Megabits per second or one and a half Megabits per second than one point five four four Megabits per second. It is not exact, but it is close enough for all but the most obnoxious purists. Similarly, an E-1 is generally described as having a transmission rate of 2 Mbps, although in reality the signaling rate is 2.048 Mbps and the payload is 1.92 Mbps. See also payload, signaling rate, and transmis- sion rate. non-blocking A switch that provides a guaranteed talk path for every terminal; in other words, there exists a 1:1 (one-to-one) relationship between ports and time slots. Such a configuration is expensive, gen- erally considered excessive and, therefore, unusual in all but the most intense applications scenarios, such as call center ACDs and backbone data switches. See Figure N-1. See also ACD, backbone, blocking, and call center. NMT 900 (Nordic Mobile Telephone 900 MHz) 338 74570c14.qxd 9/11/07 12:26 PM Page 338 Figure N-1 non-deterministic 1. Non-predictive. Referring to the inability to objectively predict an outcome or result of a process due to lack of knowledge of a cause and effect relationship or the inability to know ini- tial conditions. 2. In telecommunications switching and routing, the unpredictability of a path between nodes. See also node, path, route, and switch. 3. In local area networks (LANs) a contentious medium access control (MAC) technique that does not allow a node to predict when it will be allowed to gain access to the network. Carrier sense multiple access (CSMA), which is used in 802.3 Ethernets, is non-deterministic. See also 802.3, CSMA, deterministic, LAN, MAC, and node. non-dialable toll points A location that a caller cannot dial directly, but must call with operator assis- tance. Such locations are very remote and may be beyond the reach of cable systems and may be too low and sheltered to be reached via satellite, but can be reached via special radio circuits. In the United States, there remain a large number of non-dialable toll points, generally in deep valleys and canyons. non dispersion-shifted fiber (NDSF) See NDSF. non-facility associated signaling (NFAS) See NFAS. non-line-of-sight (NLOS) See NLOS. nonpersistent carrier sense multiple access (Nonpersistent CSMA) See CSMA. Nonpersistent CSMA (Nonpersistent Carrier Sense Multiple Access) See CSMA. non-real-time (nrt) See nrt. non real-time variable bit rate (nrt-VBR) See nrt-VBR. non-repudiation Referring to a mechanism that proves that the originating node sent a message and that the receiving node received it.Therefore, the sender cannot deny sending the message and the receiver cannot deny having received it. Non-repudiation can be effected through digital signatures, confirmation receipts, and timestamps. See also digital signature. non-return-to-zero (NRZ) See NRZ. non-wireline carrier Also known as an A Carrier.A provider of cellular radio service that is not a tra- ditional landline telecommunications services.The distinction between wireline and non-wireline carriers was made primarily for purposes of segregating bidders for radio spectrum assignment during the FCC cellular spectrum auctions.The initial approach toward spectrum assignment was designed to ensure that there was one wireline (i.e., telephone company) and one non-wireline carrier per market. See also carrier, cellular, FCC, landline, radio, spectrum, and wireline carrier. CPU Power Supply Switch 339 non-wireline carrier 74570c14.qxd 9/11/07 12:26 PM Page 339 Nordic Mobile Telephone (NMT) See NMT. normal 1. Conforming to an accepted, usual, or typical form, model, or pattern. 2. In geometry and mathematics, the transverse or perpendicular, i.e., a right angle, which is 90 degrees from a plane or sur- face. Frankly, this seems decidedly abnormal to me, as I have known a lot of people who seemed to be at right angles compared to normalcy. See also counterintuitive, critical angle, out-of-phase, and total internal reflection. North American Numbering Council (NANC) See NANC. North American Numbering Plan (NANP) See NANP. North American Time Division Multiple Access (NA-TDMA) A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS. NOS (Network Operating System) Software that provides a local area network (LAN) with multi- user, multitasking capabilities, facilitates communications and resource sharing, and thereby provides the basic framework for LAN operation.The NOS comprises modules distributed throughout the LAN, with some residing in the servers and others in the clients. See also client, client/server, LAN, and server. notation The use of signs or symbols to represent numbers, words, phrases, or even complete concepts in fields such as language, mathematics, chemistry, and music. See also binary notation and hexadecimal nota- tion. NPA (Numbering Plan Administration) The administration of the scheme of logical addresses, i.e., telephone numbers, used in the global switched telephone network (GSTN) and the national public switched telephone networks (PSTNs) that compose it.The ITU-T is responsible for international num- bering plan administration, and individual nations or regions have similar responsibilities within their domains.The North American Numbering Plan (NANP), for example, defines the telephone numbering scheme in the area loosely described as North America.The ITU-T E.164 recommendation (The Inter- national Public Telecommunication Numbering Plan) specifies the current international NPA convention at a maximum of 15 digits, although the number of digits required for calling within a nation varies. In many cases,numbering schemes vary within the same country; for example, six- and seven-digit telephone numbers coexist in Namibia and many other countries. In the countries within the NANP, the dialing scheme is +CC.NPA.NXX.xxxx, with the fields defined as follows: • + The plus sign indicates that there may be leading digits for international dialing. In the United States, the caller dials 011 as an international access code. • CC (Country Code) The country code is one, two, or three digits, established by the ITU-T.As examples, the United States is 1, South Africa is 27, and Luxembourg is 352. • NPA (Numbering Plan Area) The NPA, or area code, is a three-digit number that corresponds to a geographic area.The NPA follows the pattern NXX, with N indicating that only numbers 2–9 are allowed, as 0 or 1 would confuse the network, and X indicating that any number is allowed.The area code is used only when a call crosses an area code boundary. In such a case, the dialing sequence is 1.NNX.NNX.xxxx. N-PCS (Narrowband Personal Communications Services) See PCS. NPAC (Number Portability Administration Center) In the United States, the Federal Communi- cations Commission (FCC) established the NPAC to supervise and perform clearinghouse functions in support of local number portability (LNP) and local routing numbers (LRNs). See also LNP and LRN. NREN (National Research and Education Network) The first (1990) asynchronous transfer mode (ATM) network in the United States, NREN was a test-bed gigabit network sponsored by the Advanced Nordic Mobile Telephone (NMT) 340 74570c14.qxd 9/11/07 12:26 PM Page 340 Research Project Agency (ARPA) and the National Science Foundation (NSF). Previously (1987), a con- sortium of European carriers, end users, and universities sponsored a similar project known as the Research for Advanced Communications in Europe (RACE) project 1022 (1987). See also RACE. nrt 1. near-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time, but nearly so.That is to say the transmission must take place within a reasonably short time from the exact moment as the event itself takes place in the real world. Near-realtime QoS is essential in many applications directly involving humans and their perception of time.Transaction processing, for example, must take place in near-realtime to avoid customer dissatisfac- tion. See also QoS and realtime. 2. non-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time, that is to say that the transmission need not take place at the exact moment and in the exact sequence as the event itself takes place in the real world.Internet access, for example,need not be available instantly on demand. e-mail need not be sent across a network to be received instantly, but can tolerate a considerable level of error, latency, loss of sequence, loss of data, and retransmission. See also latency, QoS, and realtime. nrt-VBR (non real-time Variable Bit Rate) In asynchronous transfer mode (ATM), a class of traffic that is bursty, with periods of intense activity and periods of low or no activity, and of a non real-time nature that is not dependent on loss or delay because there is time to recover through retransmission.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), sustainable cell rate (SCR), maximum burst size (MBS), and burst tolerance (BT).The quality of service (QoS) parameter is cell loss ratio (CLR). ATM also defines available bit rate (ABR), constant bit rate (CBR), real-time Vari- able Bit Rate (rt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. Examples of nrt-VBR traffic include data traffic such as X.25, frame relay, transaction processing, LAN-to-LAN, and non real-time buffered voice and video traffic. See also ABR, ATM, BT, CBR, CDVT, CLR, compression, frame relay, LAN, MBS, PCR, QoS, realtime, rt-VBR, SCR, time slot, UBR, and VBR, and X.25. NRZ (Non-Return-to-Zero) A binary line coding technique in which 1 bits are represented by a high value significant condition (e.g., +V) and 0s are represented by a low value significant condition (e.g., –V), that is, opposite polarity, with no neutral or rest condition (e.g., 0V). See also line coding, Man- chester coding, and polarity. NSF (National Science Foundation) An independent agency of the United States government formed in 1950 “to promote the progress of science; to advance the national health, prosperity, and wel- fare; to secure the national defense, according to the NSF…” The mission of the NSF includes support for all fields of fundamental science and engineering. In telecommunications, the NSF has taken the ini- tiative projects such as the development of the very-high-speed Backbone Network Service (vBNS), which formed the initial backbone infrastructure for Internet2. See also Internet2 and vBNS. NT (Network Termination) In ISDN networks, a set of functions accomplished through the use of programmed logic variously embedded in the carrier network and the customer premises equipment (CPE).NT devices operate to interface the four-wire customer wiring to the physical two-wire UTP local loop, performing functions similar to those provided by digital service units (DSUs) and channel service units (CSUs) in non-ISDN digital networks. See also CPE, CSU, DSU, four-wire circuit, ISDN, NT1, NT2, and two-wire circuit. NT1 (Network Termination 1) In ISDN, the logical interface to the carrier side of the connection, performing such functions as signal conversion, synchronization, multiplexing, frame alignment, echo can- cellation, line maintenance, and performance monitoring of the local loop. Such functions correspond to Layer 1 (Physical Layer) of the OSI Reference Model. See also Echo canceller, ISDN, local loop, multiplexing, NT, NT2, OSI Reference Model, and synchronization. 341 NT1 (Network Termination 1) 74570c14.qxd 9/11/07 12:26 PM Page 341 NT2 (Network Termination 2) An interface to an intelligent ISDN-compatible device (e.g., PBX or router) responsible for the user side of the connection to the network, performing such functions as mul- tiplexing and switching. Such functions correspond to Layer 2 (Data Link Layer) of the OSI Reference Model.An NT2 commonly is actually an NT1/2 device, performing the combined functions, and oper- ating at Layers 1,2, and 3 of the OSI Reference Model. See also ISDN, NT,NT1,and OSI Reference Model. NTACS (Narrowband Total Access Communications System) A narrowband version of the TACS 1G analog cellular radio technology developed for use in the United Kingdom. NTACS operates in the 900 MHz band, employs frequency modulation (FM), and supports 400 channels of 12.5 kHz. As an analog system,TACS derives channels using frequency division multiple access (FDMA) and bidirec- tional communications is achieved through frequency division duplex (FDD) with the downlink in the 860–870 MHz band and the uplink in the 915–925 MHz band. See also 1G, analog, cellular radio, downlink, ETACS, FDD, FDMA, FM, narrowband, TACS, and uplink. NTSC (National Television Standards Committee) The initial standard (1953) for broadcast tele- vision, NTSC was named for the committee that established it in the United States. NTSC is character- ized as analog in nature, with 525 interlaced scan lines. There are 640 pixels per line, 485 of which are dedicated to the active picture.The frame rate is 30 fps, 60 fields interlaced, and the aspect ratio is 4:3.As an early analog standard that is viewed by some as overly complex and ineffective in a contemporary digital context, NTSC sometimes is referred to by its detractors in the pejorative as Never The Same Color. NTSC is defined in ITU-R Recommendation 1125 and served as the baseline for subsequent stan- dards,Phase Alternate Line (PAL) and SECAM (SÉquential Couleur Avec Mémoire). See also analog, aspect ratio, broadcast television, frame, frame rate, interlaced scanning, ITU-R, PAL, pixel, and SECAM. null 1. Valueless; amounting to nothing; zero. 2. In some computer programs, a field into which noth- ing is entered, not even a zero (0). In such programs, even a 0 can affect calculations. See also negative and positive. null modem Referring to a metallic wire cable used to connect two computers directly without the use of modems.A null modem cable simply crosses the transmit and receive wires so that the wire used by one machine for signal transmission is used by the other machine for signal reception.A null modem cable can be created by manually crossing the wires.Alternatively, a null modem adapter can be used to accom- plish the necessary crosslinks. (Note: A null modem is much less expensive and much prettier.) See also cable, modem, and wire. numbering plan administration (NPA) See NPA. Numbering Plan Area (NPA) See NPA. number portability Referring to the ability to port a number across carriers, i.e., move a telephone number from one carrier to another in a competitive environment.The United States first required num- ber portability, initially with respect to toll-free numbers.The Telecommunications Act of 1996 required local number portability (LNP). In 2003, the Federal Communications Commission required wireless number portability (WNP), extending portability to cellular telephone numbers. Number portability is possible in many countries with respect to toll-free numbers and landlines, in general. Portability is possible in fewer countries with respect to cellular service.There are restrictions, however. For example, it generally is not possible to port a number across landline and cellular domains. Neither can numbers be ported across countries. See also LNP. Number Portability Administration Center (NPAC) See NPAC. NT2 (Network Termination 2) 342 74570c14.qxd 9/11/07 12:26 PM Page 342 numerical aperture (NA) The light-gathering ability of an optical fiber, as determined by the square root of the difference of the squares of the refractive indexes of the core (n 1 ) and the cladding (n 2 ), and as expressed in the equation: NA = (n 1 2 - n 2 2 ) 1 ⁄ 2 Fiber optic transmission systems (FOTS) are based on the principle of total internal reflection, mean- ing that all light injected into the fiber is retained in the fiber.The objective is to retain all components of the optical signal in the core.However,a light source naturally injects some light rays into the core at angles less than the critical angle, which is perpendicular to the plane of the core/cladding interface. At such severe angles, the incident light rays penetrate the interface and enter the cladding, where they may be lost. The numerical aperture essentially is an indication of how well an optical fiber accepts and propagates light.As illustrated in Figure N-2, optical fiber with a small NA (top) requires more directional, i.e., colli- mated, light, whereas fiber with a large NA (bottom) does not.The higher NA allows the fiber to accept more light and propagate more modes.The NA is mathematically equal to the sine of the angle of accept- ance. Note: The NA is important in multimode fiber (MMF). It is not, however, a critical measurement in single-mode fiber (SMF), as the small core supports only a single mode of propagation and, therefore, the light is neither reflected nor refracted.The light-accepting ability can also be defined in terms of the cone of acceptance, which is the maximum angle at which the fiber will accept incident light, represented in three dimensional view. See also angle of acceptance, collimation, cone of acceptance, critical angle, MMF, SMF, and total internal reflection. Figure N-2 NXX The central office (CO) prefix, also known as the central office exchange (COE) code is a three- digit number that identifies the central office and the associated geographic carrier serving area (CSA). The CO prefix specifies the dialing pattern NXX, with N indicating that only numbers 2–9 are allowed, Cladding Normal Light Source Critical Angle Cladding Core Low NA Cladding Normal Light Source Critical Angle Cladding Core High NA 343 NXX 74570c14.qxd 9/11/07 12:26 PM Page 343 as 0 or 1 would confuse the network, and X indicating that any number is allowed.A call within an area code requires that the caller enter only the CO prefix and the line number, i.e., NXX.xxxx, unless there is an overlay area code. The line number can consist of any four digits (xxxx), and corresponds with a port on a switch that connects to a circuit or channel over a local loop that serves the physical premises of a subscriber. In the case of a cellular telephone number, there is no local loop, as such, and the number is associated with a handset, rather than a physical premises. See also CO, CSA, GSTN, NANP, overlay area code, and PSTN. Nyquist, Harry (1889–1976) A physicist and engineer at AT&T Bell Telephone Laboratories, where he did important work in areas such as thermal noise, telegraphy, facsimile systems, and television. Nyquist also did significant work that laid the foundations for information theory, as was subsequently developed by Claude Shannon. In 1928, Nyquist published a paper entitled Certain Topics in Telegraph Transmission Theory, in which he expressed what is now known as the Nyquist theorem. In telecommunications, the Nyquist theorem forms the basis for pulse code modulation (PCM), the fundamental method for convert- ing analog voice to digital format. See also Nyquist theorem and PCM. Nyquist theorem The theorem developed by Harry Nyquist and published in his 1928 paper entitled “Certain Topics in Telegraph Transmission Theory.”The Nyquist theorem states that an analog signal wave- form can be converted to digital format and be reconstructed without error from samples taken at equal time intervals if the sampling rate is equal to, or greater than, twice the highest frequency component in the analog signal.The Nyquist theorem forms the basis for pulse code modulation (PCM), the fundamental method for converting analog voice to digital format. See also Nyquist, Harry and PCM. NZDF (Non Zero Dispersion-Shifted Fiber) A type of dispersion-shifted single-mode fiber (SMF) that shifts the optimal dispersion point by adjusting the refractive index profile of the core and the cladding. There are two types of dispersion-shifted fiber (DSF). Zero Dispersion-Shifted Fiber (ZDSF) shifts the point of zero dispersion by increasing material dispersion to the point that it cancels out chro- matic dispersion at 1550 nm, rather than 1310 nm. Dense Wavelength Division Multiplexing (DWDM) and Erbium-Doped Fiber Amplifiers (EDFAs) both work in this higher window, which can create yet another noise problem in the form of four-wave mixing (FWM), a phenomenon by which wavelengths interact to create additional wavelengths.The EDFAs amplify those signals, and superimpose them on the DWDM channels. Non Zero Dispersion-Shifted Fiber (NZDF) addresses this issue by shifting the opti- mal dispersion point slightly above the range in which EDFAs operate. See also chromatic dispersion, cladding, core, dispersion, DSF, DWDM,EDFA, FWM,material dispersion, noise, refractive index, SMF, wavelength, window, and ZDSF. NXX 344 74570c14.qxd 9/11/07 12:26 PM Page 344 O1.Ohm.The ASCII symbol for ohm.The preferred symbol is Ω, but it doesn’t print easily with some software programs. 2. O+ (O positive).The most common blood type. Give blood, please. Assuming that the technician is skilled and the equipment is properly sterilized, it doesn’t take long, it doesn’t hurt, and it doesn’t make you ill, but it may very well save a life. O&M (Operations and Maintenance) Referring to all functions associated with the ongoing oper- ations and maintenance of a system or network. OADM (Optical Add/Drop Multiplexer) In wavelength division multiplexing (WDM) a device that is able to add or drop individual wavelengths without separating all wavelengths and certainly with- out converting them to electrical format. An OADM is a purely optical version of an ADM. See also ADM, wavelength, and WDM. OAM&P (Operations, Administration, Management, and Provisioning) Referring to all func- tions associated with the ongoing operation, administration, and management of a system or network, as well as its initial installation. O-Band (Original Band) The ITU-T standard optical transmission window in the wavelength range of 1,260–1,360 nm. See also wavelength and window. oblique Sloping, slanting, or indirect, i.e., neither perpendicular nor parallel. See also angle of incidence and obtuse. OBRA 93 See Omnibus Budget Reconciliation Act of 1993. obsessive compulsive disorder (OCD) See OCD. obtuse 1. In mathematics, an angle greater than 90 degrees, but less than 180 degrees. 2. A person who is slow to comprehend or understand, or who is dull or insensitive. We all know such people. See also abstruse. OC (Optical Carrier) The optical signal as defined in Synchronous Optical Network (SONET) for North America and Synchronous Digital Hierarchy (SDH) standards for international applications. All SONET levels are expressed in multiples of OC-1 (51.84 Mbps), which is a T3 signal (44.736 Mbps), or the equivalent, plus SONET signaling and control overhead, converted from electrical to optical format. The SONET digital hierarchy begins at OC-1 (51.84 Mbps) and the SDH hierarchy at OC-3 (155.52 Mbps). From OC-3, the progression of SONET and SDH levels are the same, culminating in OC-768 (39.813 Gbps). OC-1536 (79.626 Gbps) and OC-3072 (159.252 Gbps) have yet to be fully defined. See SONET for a table of OC-N levels. See also overhead, SDH, signaling and control, SONET, and T3. OCC (Other Common Carrier) The term applied in the United States prior to the breakup of the Bell System (January 1, 1984) to describe the long-distance carriers that competed with AT&T Long Lines.As a result of the Modified Final Judgement (MFJ) that caused the reorganization of the Bell System, AT&T and the OCCs became known as interexchange carriers (IXCs, or IECs) and initially were not allowed to provide intraLATA long distance service.See also Bell System, IXC,LATA, long distance, and MFJ. OCD (Obsessive Compulsive Disorder) A type of psychiatric anxiety disorder characterized by a person’s recurrent, unwanted thoughts (obsessions) and related ritualistic and repetitive behaviors (compul- sions) such as counting, checking,cleaning, or handwashing in an attempt to neutralize the obsessions.The rituals, however, provide only temporary relief and, therefore, must be repeated, again and again. By the 74570c15.qxd 9/11/07 12:26 PM Page 345 way, there are 54 words and 406 characters in this definition, including spaces and not including this sen- tence, or the following sentences in this definition.There are 84 words and 503 characters in the previous definition. Obsessive compulsive disorder comprises 3 words and 30 characters, with spaces. OCD is one word, although it really is not a word, and 3 letters, with no spaces. Personally, I prefer phrases that con- tain an even number of words and words that contain an even number of letters.Thank you. (By the way, thank you is 2 words of 5 and 3 letters, which is OK because 5 + 3 = 8, which is an even number.) OCR (Optical Character Recognition) Application software that allows a computer to recognize printed or written characters, e.g., letters, numbers, punctuation marks, and pictograms using an optical scanner for input. Optical mark recognition (OMR) also employs an optical scanner, but does not employ a character recognition engine. See also OMR. octet A unit of data eight bits in length.An octet may comprise multiple fields of data or perhaps a small portion of a field and, therefore, does not necessarily bear any relationship to a byte.A byte generally com- prises eight (8) bits that represent a letter in an alphabet (e.g., a,A, z, or Z), a diacritical mark (e.g., ~ or `), a single digit number (e.g., 0, 1, 2, or 3), a punctuation mark (e.g., , ., or !), or a control character (e.g., paragraph break, page break, or carriage return). A byte also may be four (4) bits, five (5) bits, 16 bits, or even 32 bits in length. See also byte. octothorpe See #. OD (Outside Diameter) The measure of the width of the outer surface of a circular or cylindrical object such as a hollow pipe or tube. ODU (Optical Data Unit) An entity for processing in an Optical Transport Network (OTN). An ODU comprises a frame or series of frames in their native protocol, encapsulated in a digital wrapper for network management purposes. See also digital wrapper, encapsulate, frame, network management, OTN, and protocol. OEM (Original Equipment Manufacturer) A company that builds components or products that are incorporated into products or systems sold by another company commonly referred to as a value-added reseller (VAR).An Ethernet network interface card (NIC), for example, might be built by an OEM to the specifications of a manufacturer of laptop or tablet computers. OEO (Optical-Electrical-Optical) Optical repeaters are characterized as being OEO in nature. Such a repeater receives an attenuated optical signal, converts it to an amplified electrical signal, reshapes and retimes it, converts it back to optical signal, and retransmits it. See also OOO and repeater. OFC (Optical Fiber, Conductive) The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying com- ponent, such as a metallic strength member or vapor barrier, and are not certified for use in interior plenum or riser applications. See also cable, conductor, current, optical fiber, plenum cable, and riser cable. OFCP (Optical Fiber, Conductive, Plenum) The designation by the National Fire Protection Asso- ciation (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying component, such as a metallic strength member or vapor barrier, and are certified for use in interior plenum applications. See also cable, conductor, current, optical fiber, and plenum cable. OFCR (Optical Fiber, Conductive, Riser) The designation by the National Fire Protection Associ- ation (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying component, such as a metallic strength member or vapor barrier, and are certified for use in interior riser applications. See also cable, conductor, current, optical fiber, and riser cable. OFDM (Orthogonal Frequency Division Multiplexing) Synonymous with discrete multitone (DMT). See also COFDM and DMT. OCD (Obsessive Compulsive Disorder) 346 74570c15.qxd 9/11/07 12:26 PM Page 346 offered load In frame relay, the data rate, as measured in bits per second (bps) offered to the network for delivery.The aggregate offered load can be less than the access rate supported by the access link and/or the port speed of the frame relay network device (FRND), but can never exceed whichever is less. See also access rate, data rate, frame relay, FRND, link, and port. off-hook A condition that exists when a telephone receiver or handset is lifted or removed from its cra- dle, thereby completing a circuit and placing the telephone in use.The term refers to the fact that early telephone handsets hung from a switch hook, a hook that activated a switch. See also on-hook. off-hook voice announce A key telephone system (KTS) feature that enables the system attendant to announce another incoming call even if the station user is off-hook and engaged in another call. In some implementations, the announcement is through the telephone speaker, with the station microphone muted so that the other party does not hear the announcement. In other implementations, the announcement is through the handset receiver so that the other party is not muted,as the muting is noticeable. See also KTS. off-premises extension (OPX) Synonymous with off-premises station (OPS). See OPX. off-premises station (OPS) Synonymous with off-premises extension (OPX). See OPX. offset quadrature phase shift keying (OQPSK) See OQPSK. offshoring The exporting of certain business functions to foreign countries, where either company employees or independent contractors perform the work. Offshoring commonly involves the exporting of work from developed countries to undeveloped foreign countries for reasons that include cost reduction, tax avoidance, legal liability avoidance, and strategic market expansion. If work is shifted to independent contractors, the process becomes one of offshore outsourcing. See also job security and outsourcing. OFN (Optical Fiber, Nonconductive) The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are not certified for use in interior plenum or riser applications. See also cable, conductor, optical fiber, plenum cable, and riser cable. OFNP (Optical Fiber, Nonconductive, Plenum) The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are cer- tified for use in interior plenum applications. See also cable, conductor, optical fiber, and plenum cable. OFNR (Optical Fiber, Nonconductive, Riser) The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are cer- tified for use in interior riser applications. See also cable, conductor, optical fiber, and riser cable. OH The chemical symbol for hydroxyl. See also hydroxyl. ohm (Ω) The unit of both resistance (R) and impedance (Z). In the International System of Units (SI), one (1) ohm is the resistance such that a difference in potential of one (1) volt (V) between the positive (+) end and the negative (–) end of a conductor produces a constant current of one (1) ampere (A). See also ampere, current, impedance, mho, Ohm’s Law, resistance, SI, and volt. Ohm, Georg Simon (1787–1854) The German physicist whose research on electric currents led to the formulation of Ohm’s Law. See also Ohm’s Law. Ohm’s Law V = I × R or I = V/R The law of physics that defines the relationships between power, voltage, current, and resistance in linear constant-current circuits. Ohm’s Law states that the current (I) in an electric circuit is directly proportional to the electromotive force (emf), or voltage (E), applied to a cir- cuit, and inversely proportional to the resistance (R) of the circuit.Another way of thinking of Ohm’s Law is that the current flowing through a wire is directly proportional to its cross-sectional area and inversely proportional to its length. So, for a circuit of a given metal at a given constant temperature, the thicker and shorter the wire, the less the resistance. Ohm’s Law is named for Georg Simon Ohm, its inventor. See also current, emf, resistance, and voltage. 347 Ohm’s Law 74570c15.qxd 9/11/07 12:26 PM Page 347 [...]... developed and promoted by the Personal Computer Memory Card International Association (PCMCIA) PC cards are approximately the length (86.5 mm) and width (54 mm) of a credit card, but 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 3 67 3 67 PCMCIA card much thicker, and fit into a slot built into a laptop or tablet personal computer (PC) or peripheral.Type I cards are 3.3 mm thick and are used for add-in random access... at the Network Layer, a packet, and at the Application Layer, a message See also bit stream, frame, message, overhead, packet, payload, protocol stack, and protocol suite 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 370 PE (Phase Encoding) 370 PE (Phase Encoding) More commonly known as phase-shift keying (PSK) See PSK peak cell rate (PCR) See PCR pedant A person who puts unnecessary emphasis on minor or trivial... vision is controversial See also phi phenomenon Personal Access Communications Services (PACS) See PACS personal area network (PAN) A wireless personal area network (WPAN) See WPAN 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 371 371 phase personal communications network (PCN) See PCN personal communications services (PCS) See PCS (1) Personal Communications Services (PCS) See PCS (2) Personal Communications... relationship between the positions of a signal at two instants in time In other words, phase is a measurement of the relative position of a waveform at a significant instant of the 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 372 phase 372 signal relative to a time scale Phase is measured in degrees (°), with a full oscillation expressed as 360°, as illustrated in Figure P-3 The phase of a signal can shift unintentionally,... brand spoofing and carding A popular Internet e-mail scam that involves unsolicited e-mail (i.e., spam) contact in which the scam artist attempts to gain valuable information from the 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 373 373 photon target by gaining that person’s confidence through various social engineering techniques and technical subterfuge.The term phishing was coined in the 1996 timeframe by crackers... ground into pulp), if we had not advanced beyond the paper office of the 1960s However, we still print hard copies of electronic documents, and seem to consume more paper with each passing year So much for the paperless office See also lead balloon 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 362 parabolic antenna 362 parabolic antenna An antenna comprising a parabolic reflector with a transmitting and receiving... in Table O-2, alongside their corresponding SDH/SONET line rates Table O-2: G .70 9 Line Rates and Corresponding SDH/SONET Line Rates G .70 9 SDH/SONET Interface Line Rate OC/STM Level Line Rate OTU-1 2.666 Gbps OC-48/STM-16 2.488 Gbps OTU-2 10 .70 9 Gbps OC-192/STM-64 9.953 Gbps OTU-3 43.018 Gbps OC -76 8/STM-256 39.813 Gbps G .70 9 also specifies an interface for 10 GbE clients, utilizing the same digital... desirable, the electronic module is employed See also attenuation, cross-connect, dispersion, DXC, OC-3, OC-12, OC-48, OEO, OOO, optical, protocol, regenerator, SDH, signal, and SONET 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 3 57 P 1 Peta (P), from the Greek penta, meaning five, translates to quadrillion, referring to the fact that, in terms of order of magnitude in base 1,000, Peta is 1,0005 In order, that... in the 1920s, through the 1930s, and remained in service until the late 1 970 s, at which point they were replaced by electronic common control (ECC) switches See also ECC and SxS PANS (Pretty Advanced New Services, Pretty Advanced Network Services, Peculiar And Novel Services) A term that appeared in the 1 970 s to distinguish new PSTN services from POTS (Plain Old Telephone Service) PANS includes custom... Layer, Physical Layer, Presentation Layer, protocol, Session Layer, SNA, software, standard, subnetwork, TCP/IP, Transport Layer, X.200, and x series 74 570 c15.qxd 9/11/ 07 12:26 PM Page 353 353 OTN (Optical Transport Network) OSP (OutSide Plant) All of the telecommunications apparatus and cable systems outside (i.e., not housed in buildings) such as central offices or customer premises OSP includes all . Simon Ohm, its inventor. See also current, emf, resistance, and voltage. 3 47 Ohm’s Law 74 570 c15.qxd 9/11/ 07 12:26 PM Page 3 47 OLT (Optical Line Terminal) In a passive optical network (PON), the device. Appli- cations, standardized as P.563 See also ITU-T, P.862, PAMS, PESQ, and toll quality. 74 570 c16.qxd 9/11/ 07 12: 27 PM Page 3 57 . TCP/IP, Transport Layer, X.200, and x series. oscillator 352 74 570 c15.qxd 9/11/ 07 12:26 PM Page 352 OSP (OutSide Plant) All of the telecommunications apparatus and cable systems outside (i.e.,